In microscopes, particularly in light microscopes for observing objects with the bright-field transmitted light contrast procedure, a microscope beam path is directed from a bright-field light source through the object and through the microscope objective into the microscope tube.
Microscopes that are further developed for observing the object in the incident-light fluorescence contrast procedure also have a fluorescence system comprising essentially the following components:                a multispectrally emitting light source, such as an HBO arc lamp with a line spectrum, or        an XBO arc lamp with a continuous spectrum, or        a light source that emits over a narrow band, such as a LED (light-emitting diode), and        optical elements to image the light source in the object,        excitation filters to select the color of the illumination,        a beamsplitter, and        emission filters to select the color for imaging of the object.        
The light source is usually placed outside the microscope structure and coupled through an illumination connection. A set of excitation filters is placed in a mechanical changing means, such as a revolver or a slide moving transversely to the optical axis, so that the excitation filters can be placed in the illuminating beam bath, depending on their optical properties and on the object properties. Likewise a set of emission filters.
When the light source is an arc lamp, a shutter is provided to interrupt the illuminating light. When a LED is used as the light source, the illuminating light can [be controlled] by switching the operating voltage for the LED on and off.
The microscope can be changed from operating in the incident-light fluorescence contrast procedure to the bright-field transmitted light contrast procedure by, for example, setting the changing means for the filter sets to a blank position, so that the illuminating light coming from a bright-field light source can pass unfiltered. At the same time, the shutter is closed, or the operating voltage for the fluorescence excitation light source is interrupted and the bright-field light source is switched on. The bright-field light source can at the same time be adjusted to a preset brightness.
The present invention refers particularly to fluorescence systems with one or more LEDs as the light source for the incident-light fluorescence illumination.
Microscopes constructed in this manner are known principally from two manufacturers.
One of those is the company “FRAEN CORPORATION S.r. 1.; Via Stelvio, 12; 20019 Settimo Milanese—MI”.
In that case, the change between incident-light fluorescence contrast and bright-field transmitted light contrast is accomplished by sliding a mirror into or out of the beam path, so that when the mirror is pushed in the object is illuminated by an LED in incident-light fluorescence and when the mirror is pulled out the object is illuminated by the bright-field light source in bright-field transmitted light. At the same time the mirror is moved, the LED must be switched on or off and a filter slide must be moved back and forth to change between a filter position and a blank position.
The fluorescence unit is designed as an add-on for light microscopes which by themselves are operated with the transmitted light procedure and are operated manually. This add-on system has the disadvantage that it is relatively complicated. In addition, four hand operations are needed every time to change between incident-light fluorescence contrast and bright-field transmitted light contrast.
In the applicable microscopes of the second manufacturer, the company “EUROIMMUN AG”, Seekamp 31, D-23560 Lübeck”, the incident-light fluorescence contrast operating mode is selected by sliding a filter set into the illumination beam path while simultaneously switching on a LED as the light source for the fluorescence excitation.
In this case, three hand operations are needed every time to change between incident-light fluorescence contrast and bright-field transmitted light contrast. There is a further disadvantage that because of a mechanical separation of a solidly built-in filter set and a solidly built-in light source it is impossible for the customer to select different fluorescence wavelengths.
Because of that, the object of the invention is to make possible, for a microscope of the type initially described, a less time-consuming but ergonomically improved change between incident-light fluorescence contrast and bright-field transmitted light contrast and the reverse.